Method of coloring aluminum



4 Patented Au 21, 1934 i 1,971,240

, UNITED STATES PATENT OFFICE 1,971,240 METHOD OF COLORING ALUMINUMMartin Tosterud, Arnold, Pa., assignor to Aluminum Company of America,Pittsburgh, Pa., a corporation of Pennsylvania No Drawing. ApplicationDecember 1'1, 1930,

, Serial No. 502,987

4' Claims. (01. 148.-6)

This invention relates to the treatment of alkali carbonates and solubledichromates, and 1 aluminum and aluminum alloy surfaces to prouse bothin the preferred practice of the invenduce thereon a colored coating.The term alumition. A solution of any alkali carbonate and any num, asused herein and inthe appended claims, soluble dichromate may be used,but I prefer 5 includes that metal in every degree of purity and asolution of sodium carbonate and potassium 60 all alloys thereofcontaining sufficient aluminum dichromate containing about 0.5 to 6 percent of to permit the formation of a suitable oxide coatthe carbonateand about 0.1 to l per cent of the ing on the surface of the article, asexplained dichromate, and! have had excellent results with hereinafter,that is to say, alloys in which the about 2 per cent of the former andabout 0.5 10 aluminum content is 50 per cent, approximately, per cent ofthe latter. Simple immersion of the 65 or more. piece to be coated inthe treating solution, or The many and varied uses of aluminum in bothspraying it with the solution, is in general sufthe practical anddecorative arts have made very ficient without the application of anyexternal desirable the development of suitable process by electricalenergy. which aluminum surfaces may be colored, and the After thedesired oxide coating has been formed 7c I provision of such a processis one of the objects on the aluminum surface I treat the coated metal,of my invention. A further object is to provide say by immersion orspraying, with a solution a process which is simple in operation andwhich of a soluble salt of permanganic acid. While I may be practiced.on a large scale with reasonable prefer to use potassium or sodiumpermanganate, cost and a minimum of difiiculty. any soluble salt ofpermanganic acid may be used is In the course of an extensiveinvestigation f r h p rp T concentration of h p directed toward thedevelopment of suitable procma ga Solution (1085 ot appear to be a 65595and th d for th coloring f th critical factor, as I have found thatsolutions faces of aluminum and its alloys, 1 have 115- containing as11131316 as 1 per cent Of the soluble covered that certain colors areparticularly dif- Compound Compounds used, and Solutions 80 ficult toobtain on aluminum. Thus the pro which are completely-saturated, willproduce the duotion of a, brown color, which color is often COlOI'Sdesired. I prefer to use concentrated so1udesired on aluminum surfaces,is one which p tions, however, since I have observed that the gentsparticular difiioulty S h @1013 h adsorption of the solution by theoxide coating can be readily obtained by my present i ti is more rapidthan with dilute solutions. I have 5 which, briefly stated, comprisesfirst treating the further determined that the temperature of thea1uminum 31131913 to provide on its surface a, solution (if the salt Ofpermanganic acid at the hard and to a substantial degree adsorbed oxidee at W h the Oxide-coated metal is introcoating and thereafter treatingthis coating with du therein is not a governing m t r and that asolution of a soluble salt ofpermanganic acid. Satisfactory c010rs maybe P e Whether the on According to the preferred practice of th solutionbe cold or hot. The use of a hot solution invention the aluminum articleis first treated to facilitates d y f the article afterwards. produceupon its surface an oxide coating which As has hereinabove beenmentioned, the color is hard and dense and which has sufficient adpr d don h l m n m r al mi um all y sorbent qualities to retain, when immersedin or urf c in h pr t of my novel method is e equivalently treated witha liquid, an apprebrown or some shade thereof, and l have found ciablequantity of such liquid within and upon that the depth of color and theparticular shade it. The term oxide coating, as used herein, desired maybe regulated by varying the thiclz1- is a well known designation in theart to deness of the oxide coating which is originally 5 scribe a layerof aluminum oxide artificially proproduced on the aluminum or aluminumalloy mg duced on the aluminum or aluminum alloy sursurface. If thealuminum, in the oxide-coating faces by chemical treatment, with orwithout process, is immersed in the solution for a brief the use ofexternally applied electrical energy, period, a thin film of oxidecoating will be obbut the term does not include the thin film of tained.With longer immersions, the thickness 0 aluminum oxide which isnaturally formed upon of this oxide coating increases and in thisway 105the metal by contact with the air. a satisfactory adherent, adsorbentoxide coating In the various methods of producing oxide of the desiredthickness may be produced, adeeper coatings, there are certain reagentswhich i have color and darker she de being, in general, profoundparticularly effective for the purpose duced with a heavy coating thanwith a thin of my present invention. These reagents are coating. m

As a specific example of the method in which my invention may bepracticed, an aluminum article was immersed for 10 aqueous solutioncontaining 20' grams per liter of sodium carbonate and 5 grams per literof potassium dichromate. -At the end of this time, the metal was removedfrom the solution, washed, and while in a moist condition immersed in ahot saturated solution of potassium permanganate for a period of 2 to 5minutes. The article, after removal from the permanganate solution anddrying, had on its surface a brown color which, for all practicalpurposes, was stable and permanent and completely adsorbed in the oxidecoating.

I am aware that it has been proposed to impart a brown or black colortov porous articles by successive treatments with separate reagents, onean oxidizable compound and the other potassium permanganate to oxidizethe same. In my invention I produce the brown color by treating theoxide coating with potassium permanganate or other permanganic compoundwithout prior, or subsequent treatment.

I do not claim herein broadly the coloring of aluminum by adsorbing, inan adsorbent oxide coating on the surface of the metal, successivereagents which react in the coating to precipitate a colored inorganiccompound, but .do so in my copending application Serial No; 474,665,filed August 11, 1930.

It is to be understood that the invention is not limited to the specificdetails herein described M No- 1.911.240.

to 15 minutes in an CERTIFICATE OF CORRECTION.

but may -be carried out in other ways without departure from its Iclaim- 1. The method of permanently coloring the surfaces of aluminum oraluminum alloy articles, comprising treating the metal surface with asolution containing an alkali carbonate and a soluble dichromate to formthereon an adsorbent oxide coating, and thereafter without furthertreatment impregnating the coating with a soluble salt of permanganicacid.

2. The method of permanently coloring the surfaces of aluminum oraluminum alloy articles, comprising forming onthe metal surface anadsorbent oxide coating, and thereafter without further treatmenttreating said surface with a solution of potassium permanganate, for thepurpose herein described.

3. The method of permanently coloring the surfaces of aluminum oraluminum alloy 'articles, comprising treating the metal surface with asolution containing an alkali carbonate and a soluble dichromate to formthereon an adsorbent oxide coating, and thereafter without furthertreatment treating the coating with a solution'of potassiumpermanganate, for the purpose herein described.

4. The method of permanently coloring aluminum or aluminum alloy byimpregnation of an spirit.

adsorbent oxide coating previously formed on the surface of the metal,which consists in immersing the article in a solution of a salt ofpermananic acid. MARTIN TOSTERUD.

magnet 21.

MARTIN TOSTERUD.

It is hereby certified that error appears in the printed specificationoftheabove numbered patent "adsorbed" read adsorbent; this correctiontherein that the Patent Office.

requiring correction as mum: Page 1, line": 33.1w

and that the" said Letters Patent should be read with the same mayconform to the record ofthe case in Signed and sealed this- ZSthday ofseptelnber, A. o. .1934. l

(Seal) 4 Leslie Frazer Acting Commissioner of Patents,

As a specific example of the method in which my invention may bepracticed, an aluminum article was immersed for 10 aqueous solutioncontaining 20' grams per liter of sodium carbonate and 5 grams per literof potassium dichromate. -At the end of this time, the metal was removedfrom the solution, washed, and while in a moist condition immersed in ahot saturated solution of potassium permanganate for a period of 2 to 5minutes. The article, after removal from the permanganate solution anddrying, had on its surface a brown color which, for all practicalpurposes, was stable and permanent and completely adsorbed in the oxidecoating.

I am aware that it has been proposed to impart a brown or black colortov porous articles by successive treatments with separate reagents, onean oxidizable compound and the other potassium permanganate to oxidizethe same. In my invention I produce the brown color by treating theoxide coating with potassium permanganate or other permanganic compoundwithout prior, or subsequent treatment.

I do not claim herein broadly the coloring of aluminum by adsorbing, inan adsorbent oxide coating on the surface of the metal, successivereagents which react in the coating to precipitate a colored inorganiccompound, but .do so in my copending application Serial No; 474,665,filed August 11, 1930.

It is to be understood that the invention is not limited to the specificdetails herein described M No- 1.911.240.

to 15 minutes in an CERTIFICATE OF CORRECTION.

but may -be carried out in other ways without departure from its Iclaim- 1. The method of permanently coloring the surfaces of aluminum oraluminum alloy articles, comprising treating the metal surface with asolution containing an alkali carbonate and a soluble dichromate to formthereon an adsorbent oxide coating, and thereafter without furthertreatment impregnating the coating with a soluble salt of permanganicacid.

2. The method of permanently coloring the surfaces of aluminum oraluminum alloy articles, comprising forming onthe metal surface anadsorbent oxide coating, and thereafter without further treatmenttreating said surface with a solution of potassium permanganate, for thepurpose herein described.

3. The method of permanently coloring the surfaces of aluminum oraluminum alloy 'articles, comprising treating the metal surface with asolution containing an alkali carbonate and a soluble dichromate to formthereon an adsorbent oxide coating, and thereafter without furthertreatment treating the coating with a solution'of potassiumpermanganate, for the purpose herein described.

4. The method of permanently coloring aluminum or aluminum alloy byimpregnation of an spirit.

adsorbent oxide coating previously formed on the surface of the metal,which consists in immersing the article in a solution of a salt ofpermananic acid. MARTIN TOSTERUD.

magnet 21.

MARTIN TOSTERUD.

It is hereby certified that error appears in the printed specificationoftheabove numbered patent "adsorbed" read adsorbent; this correctiontherein that the Patent Office.

requiring correction as mum: Page 1, line": 33.1w

and that the" said Letters Patent should be read with the same mayconform to the record ofthe case in Signed and sealed this- ZSthday ofseptelnber, A. o. .1934. l

(Seal) 4 Leslie Frazer Acting Commissioner of Patents,

